Field of the Invention
The present invention relates to a touch device for determining real coordinates during detecting raw coordinates of the multiple touch points and method thereof.
Description of the Related Art
During the recent two decades, touch technologies have gained acceptance in a variety of consumer applications, such as touch screens in ATMs (automated-teller machines), track pads in laptop computers, and scroll wheels in media players. In these consumer applications, the movement of an object such as a finger or a stylus along a surface of a touch sensor is detected by the touch sensor to generate electrical signals for the subsequent processes.
There are many types of touch sensing methods, such as resistive sensing type, capacitive sensing type, acoustic wave sensing type, optical sensing type and the like. For the capacitive sensing method, the touch sensor perceives touch locations by detecting the change in capacitance due to the proximity of a conductive object such as metal or a part of human body. The capacitive touch sensors are classified into a projective capacitive type and a surface capacitive type. The projective capacitive touch sensor contains a lattice electrode pattern, while the surface capacitive touch sensor includes electrodes formed on peripheral edges of a continuous conductive sheet.
FIG. 1 and FIG. 2 show a conventional projective capacitive touch panel 1 comprising a plurality of first electrodes 2 in the first direction, a plurality of second electrodes 3 in the second direction, an insulator 4 and a substrate 5. The plurality of first electrodes 2 and the plurality of second electrodes 3 are intersected with each other to form a lattice pattern placed on the substrate 5. The insulator 4 is arranged between the plurality of first electrodes 2 and the plurality of second electrodes 3. Besides, a processor (not shown) is connected to the plurality of first electrodes 2 and the plurality of second electrodes 3. When a conductive object such as a finger or stylus is touching or moving on the projective capacitive touch panel 1, the change in self capacitance produced on both first electrodes 2 in the first direction and second electrodes 3 in the second direction can be transmitted and then processed by the processor. The centroids of the change in self capacitance indicate the locations of the touch point in the first direction and the second direction of the projective capacitive touch panel 1. The coordinate of the touch point is calculated by intersecting the centroids in the first direction and the second direction. In other words, the conventional method of detecting touch point comprises: (a) scanning both the first electrodes 2 in the first direction and the second electrodes 3 in the second direction; (b) computing centroids of the change in self capacitance in the first direction and the second direction; and (c) calculating the coordinate of the touch point based on the centroids.
FIG. 3 shows that when two touch points C, D appear on the surface of the projective capacitive touch panel 1, two centroids 6a, 6b will be detected on the first electrodes 2, while two centroids 7a. 7b will be detected on the second electrodes 3. Thus, four raw coordinates C(6a,7a), D′(6a,7b), D′(6b,7a) D(6b,7b) are formed, two of which are real coordinates and the other two are ghost coordinates.
The acoustic touch sensor comprises an element for emitting sound wave and another element for receiving the sound wave, which causes the sound waves to be transmitted across the surface of the touch sensor. The touch of an object absorbs some energy of the wave, which can be detected at the touch location. The optical touch sensor works in the similar way to the acoustic touch sensor, except that the wave transmitting along the surface is light wave such as infra-red wave. Drawing on the above sensing method, the acoustic touch panel and the optical touch panel could use sensing paths in two directions to calculate the coordinate of the touch point. Thus, when more than one touch points present on the acoustic or optical touch panel, the ghost coordinates will be inevitable.
As a result, the conventional projective capacitive touch panel, the acoustic touch panel, or the optical touch panel would have the appearance of the ghost coordinates that limits the application and operation of these touch panels for determining multiple touch points. Therefore, it is necessary to eliminate ghost coordinates during the process of determining multiple touch points on those touch panels mentioned above.